1. Technical Field of the Invention
The present invention relates to an imaging system for a motor vehicle, and in particular to an imaging system in which detected infrared radiation is processed by a digital signal processor in order to visually enhance road conditions based upon temperature.
2. Description of the Prior Art
Poor visibility at night results from a number of causes that have conspired to make traveling after dark a potentially troublesome situation. A typical driver uses low beam head lamps in most driving conditions after dark. Low beams, however, have a limited range and can illuminate a relatively small portion of the road ahead. Moreover, most drivers have experienced the temporary blinding effect caused by the head lamps of oncoming vehicles. The scattering of light is worsened in wet conditions due to the reflective surface of the roads. Rain, snow, fog and other types of inclement weather further limit visibility at night.
As a result of reduced visibility at night, engineers turned to other means of visualization that involved detecting radiation that is otherwise invisible to the human eye. All objects are, to a greater or lesser extent, both emitters and reflectors of radiation. There is a correlation between the temperature of an object and the wavelength of radiation emitted by that object, a principle known as black body radiation. For objects having a temperature between 0xc2x0 and 50xc2x0 C., as is most common in everyday experience, the radiation emitted is in the infrared band of the spectrum. Even though an object is not reflecting visible light that same object is likely emitting infrared light. Scientists and engineers created a means of detecting infrared radiation thereby permitting the visualization of otherwise invisible objectsxe2x80x94a night vision system.
One such night vision system is known as thermal imaging. Developed by the military, thermal imaging was once thought to be too expensive and cumbersome for use in the consumer vehicle market. However, recent advances in electronics and infrared detectors have made the use of night vision in consumer vehicles more tenable, and at least one manufacturer recently incorporated thermal imaging system into a vehicle.
Both passive and active imaging systems exist. A passive system is not unlike the human-eye in that it primarily detects radiation that is emitted from objects. On the other hand, an active system projects radiation and then primarily detects the reflection of that radiation off of objects. Passive systems have several advantages over their active counterparts. Most importantly, passive systems do not project any kind of radiation from the vehicle, and thus will not interfere with the surrounding environment or with the imaging systems of other vehicles. A far infrared camera is an example of a passive system, and it is the infrared camera utilized in the present invention.
In general, a far-infrared camera detects radiation in the 7 to 14 micron wavelength band. This wavelength band corresponds to a temperature range of approximately xe2x88x9220xc2x0 to 50xc2x0 C. that covers all objects that are of interest to automotive engineers. The human body, for example, has a peak emission at approximately 9.3 microns, which corresponds to the human body temperature of about 37xc2x0 C.
A consumer vehicle thermal imaging system is typified by the Cadillac Deviled Thermal Imaging Night Vision System by General Motors. The Cadillac system consists of a thermal imaging camera, a heads-up display, and image controls. As in other thermal imaging systems, the Cadillac system uses a camera to capture infrared data, the camera electronics to process the data, and a heads-up display to present the information to the driver.
Despite the Cadillac system improving night driving conditions, there remains a persistent problem in the resolution and contrasting of the infrared image. Although a standard far-infrared camera can detect incremental temperature ranges over a wide range of temperatures, the image presented to the driver does not adequately reflect subtle distinctions between objects. Most importantly, existing imaging systems cannot distinguish the road boundary from the road, nor can they distinguish the lane markers that separate traffic from the road.
Thus, there is a need for a far-infrared imaging system for use in a vehicle that enhances the relative temperature distinctions between objects such that a driver will be presented with a complete representation of the road conditions, including the road boundaries and lane markers.
The present invention is an infrared imaging system that comprises a far-infrared camera disposed at the front end of a vehicle adapted for detecting thermal radiation in the 7 to 14 micron wavelength band and producing an image signal indicative of the temperature of the surrounding objects. A digital signal processor receives the image signal and selectively enhances the temperature resolution based upon the relative temperature distribution of the image signal, which is proportional to the temperature of objects emitting in the infrared region. A display apparatus receives a display signal that is temperature enhanced, or temperature warped, and displays that signal to the driver.
The far-infrared camera detects thermal radiation and produces an image signal indicative of the temperature of the objects, the image signal having selected temperature concentrations depending on the wavelength of the radiation emitted. A digital signal processor receives the image signal, calculates the temperature distribution of the signal, and selectively discriminates between temperature concentrations based upon the temperature distribution such that large temperature concentrations are mapped from the image signal to a display signal in which the resolution and differences in temperature are more evident to the driver. The display apparatus is disposed within the vehicle such that the vehicle operator is informed of the driving conditions ahead.
The present invention also provides a method for enhancing the thermal imaging resolution of an infrared camera for a vehicle. The method comprises receiving thermal radiation and producing an image signal in response thereto, calculating the concentrations of radiation, and mapping the high concentrations of radiation into a display signal thereby thermally enhancing the display signal. The display signal is then displayed to the vehicle operator such that the vehicle operator can visually detect subtle distinctions in the road features, including the road boundary and lane markers as well as pedestrians.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.